1. Field of the Invention
This invention relates, generally, to devices that hold concrete reinforcing bars to prevent them from slipping. More particularly, it relates to a joint that includes a wedge and teeth to firmly grip said bars.
2. Description of the Prior Art
Concrete reinforcing bars are more commonly known as rebars. They are used in the construction industry in footers and in other concrete applications to strengthen the concrete.
Rebars often slip out of position when concrete is poured, and their effectiveness is thereby reduced. Accordingly, inventors have created devices designed to hold rebars against movement. Examples of earlier work in this field are shown in U.S. Pat. Nos. 4,695,178 and 4,997,306.
FIG. 8 of the present disclosure shows a prior art rebar joint of oblong construction that holds the leading end of a first rebar 10-a and the trailing end of a contiguous rebar 10-b in parallel relation to one another. A pair of axially aligned bores 3-a, only one of which is shown, are formed in the joint 2 and a wedge 6 is driven into said bores after the rebars have been inserted into the open opposite ends of the joint. The wedge drives each rebar into frictional engagement with an internal side wall of the joint.
The FIG. 8 joint is more effective than no joint at all, but it has been found that the rebars still slip at least to some extent when the joint is in use. How such slippage could be overcome is not apparent to those of ordinary skill in this art.
A second prior art joint is shown in FIG. 9. This joint 2 receives rebars 10-a and 10-b in axial alignment with one another. Joint 2 has a "U" shape and includes elongate parallel side walls 1-a and 1-b having a plurality of cooperatively aligned bores 3-a and 3-b formed along the longitudinal extent thereof, respectively. Each of said bores receives a two part wedge having a first part denoted 6 and a second part denoted 9. Part 9 is flanged to limit the depth of its penetration.
In both of these prior art embodiments, the application of an axially directed tensile force to the joined rebars that is far below the tensile strength of the rebars will successfully pull the rebars from the joint.
Note in FIGS. 8 and 9 that the surfaces of the rebars are somewhat smooth. Rebars having rougher surfaces have been tried, in the hope that the frictional force between a rough surface and the inside walls of the joints might increase, but the opposite has been found to be true, i.e., when a pair of rough surface rebars are joined in the devices of FIGS. 8 and 9, even less axially directed tensile force is required to separate them from the joint. This is because the amount of surface area available for frictional contact is even less when rough rebars are joined. Thus, the problem of joining rebars together appears intractable and those of ordinary skill in the art have been unable to solve it.
The prior art, when considered as a whole in accordance with the requirements of law, neither teaches nor suggests to those of ordinary skill in this art how the seemingly intractable problem of rebar slippage could be solved.